The present disclosure relates to a memory unit that includes memory elements storing information by change of electric characteristics of a memory layer and a method of operating the memory unit.
In information apparatuses such as a computer, a DRAM (Dynamic Random Access Memory) with a high-speed operation and high density is widely used as a random access memory. However, in the DRAM, the manufacturing cost is high since the manufacturing process is more complicated than that of a general logical circuit LSI (Large Scale Integrated Circuit) and a general signal processor used for electronic apparatuses. Further, since the DRAM is a volatile memory in which information is not retained if the power is turned off, it is necessary to perform refresh operation frequently, that is, it is necessary to read out written information (data), amplify the information again, and rewrite the information.
Meanwhile, in recent years, what we call bipolar type resistance random access memories that record low resistance state and high resistance state according to current direction have been developed. Further, what we call 1T1R type (including one memory element for one transistor) nonvolatile memory cells composed of combination of such a bipolar type resistance random access memory and a selection transistor have been proposed as well. For example, in “A Novel Resistance Memory with High Scalability and Nanosecond Switching” (Technical Digest IEDM2007, pp. 783-786) by K. Aratani and more 12 authors, a new type resistance random access memory particularly advantageous to microfabrication limit of memory elements is proposed.